Folate metabolism gene 5,10-methylenetetrahydrofolate reductase (MTHFR) is associated with ADHD in myelomeningocele patients.

The objective of this study was to examine the relation between the 5, 10-methylenetetrahydrofolate reductase (MTHFR) gene and behaviors related to attention- deficit/hyperactivity disorder (ADHD) in individuals with myelomeningocele. The rationale for the study was twofold: folate metabolizing genes, (e.g. MTHFR), are important not only in the etiology of neural tube defects but are also critical to cognitive function; and individuals with myelomeningocele have an elevated incidence of ADHD. Here, we tested 478 individuals with myelomeningocele for attention-deficit hyperactivity disorder behavior using the Swanson Nolan Achenbach Pelham-IV ADHD rating scale. Myelomeningocele participants in this group for whom DNAs were available were genotyped for seven single nucleotide polymorphisms (SNPs) in the MTHFR gene. The SNPs were evaluated for an association with manifestation of the ADHD phenotype in children with myelomeningocele. The data show that 28.7% of myelomeningocele participants exhibit rating scale elevations consistent with ADHD; of these 70.1% had scores consistent with the predominantly inattentive subtype. In addition, we also show a positive association between the SNP rs4846049 in the 3'-untranslated region of the MTHFR gene and the attention-deficit hyperactivity disorder phenotype in myelomeningocele participants. These results lend further support to the finding that behavior related to ADHD is more prevalent in patients with myelomeningocele than in the general population. These data also indicate the potential importance of the MTHFR gene in the etiology of the ADHD phenotype

Allele frequency of seven SNPs in the <i>MTHFR</i> locus of White and Hispanic MM individuals in the study.

<p>Notes: rs – reference identification number of SNPs in the dbSNP database, Func. – functional significance of SNP, A1 – common allele of SNP, A2 – rare allele of SNP, N – number of subject successfully genotyped, Freq. – frequency of A1/2, HWE – Hardy Weinberg Equilibrium test result, NS – not significantly deviated from Hardy Weinberg Equilibrium (p>0.05). Additional samples were genotyped for rs1801133 and rs1801131 because these two SNPs have previously been examined with suggested association to ADHD <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0051330#pone.0051330-Krull1" target="_blank">[42]</a>.</p

Case-Control Analyses of ADHD phenotypes in White subjects with MM.

<p>Note: N – number of subjects successfully genotyped. Cases are MM individuals testing positive for ADHD, controls are MM individuals testing negative for ADHD. Significant p-values ≤0.05 are indicated by bold lettering. Empirical p-value is the p-value obtained through random permutation of the experimental data to evaluate the effect of multiple testing.</p

Simplified schematic of the folic acid metabolic cycle.

<p>Folate receptors transport dietary folate into cells and the folate is converted into dihydrogolate (DHF) then tetrahydrofolate (THF) by dihydrofolate reductase (DHFR). In the folate metabolic cycle, THF is converted to 5,10-methyleneTHF, a substrate of 5,10-methyleneTHF reductase (MTHFR), then to 5-methylTHF. 5-methylTHF can be recycled by methionine synthase/methionine synthase reductase (MTR/MTRR) to THF and methionine. Alternatively, 5-methylTHF can be use to synthesize purine. The Methionine can be used in the methionine cycle to produce S-Adenosyl-methionine (SAM), S-adenosyl-homocysteine (SAH) and homocysteine. Conversion of SAM to SAH requires betaine, a product of choline metabolism. SAM is a major cellular methylation agent for DNA, RNA, protein, and phospholipids.</p

Genomic structure of the <i>MTHFR</i> gene and the location of the seven SNPs examined in this study.

<p>Shaded boxes represent the exons (1 to 12) of <i>MTHFR</i> gene and the line in between represent intron regions. Distances and locations are approximate.</p

Linkage disequilibrium analysis of rs4846049 versus the other six SNPs tested.

<p>Notes: Chr1 – Chromosome 1, Loc. – location in bases from p-arm of chromosome 1 with reference to human genome sequence GRCH37/hg19 assembly, r∧² – correlation coefficient between SNP1 and SNP2, a value ≥0.8 suggests linkage disequilibrium.</p

Haplotype analyses of <i>MTHFR</i> SNPs and ADHD in White subjects with MM.

<p>Notes: Haplotypes are generated by Haploview 4.2, freq – frequency of haplotypes, ADHD –Attention Deficit Hyperactivity Disorders.</p>*<p>results of 10,000 permutations were performed using Haploview4.2 on. Significant p-values ≤0.05 are indicated by bold lettering.</p

Ethnicities of individuals in the study.

<p>Ethnicities of individuals in the study.</p

White and Hispanic MM individuals genotyped.

*<p>– other SNPs include rs3737965, rs2066470, rs9651118, rs2274976, and rs4846049.</p